Photographic elements generally comprise hydrophilic binders, e.g., gelatin as vehicles for the image chemistry and in the protective overcoat. These hydrophilic colloids can absorb moisture and become tacky in humid environments and at elevated temperatures causing the photographic materials to stick to each other, for example, if packed in a stack. To eliminate these difficulties, it is conventional to incorporate finely divided powdered grains or matting agents (beads) into the protective layer to increase the surface roughness and prevent contact and subsequent sticking. It is desirable that these matte beads are non-hydrophilic and consequently they are composed of materials different from the hydrophilic binders. Thus, they typically have a different refractive index. When light is passed through the photographic element, such as in photographic printing or projection, both the increased surface roughness and difference in refractive index causes a non-uniform light path and results in graininess in photographic prints or mottle in projected images. For these reasons, manufacturers have been using a large amount of processing removable (soluble) mattes, designed to solubilize in high pH solutions, in combination with a small amount of process surviving (permanent) matte. High concentrations of processing removable matte are used especially when the unprocessed photographic elements are used or stored at high relative humidity and at elevated temperatures of from 30.degree. to 40.degree. C. High concentrations of soluble matte are also used to prevent contact specks which cause adverse sensitometric defects when the materials are rolled up.
The use of a high level of processing removable matte provides a satisfactory solution to conventional films for amateur use, for which the processed, or developed, film strips are returned to the consumer in synthetic resin pouches, or sleeves, where the front side and back side of the film do not come in contact with each other.
Recent patents have disclosed photographic systems where the processed element may be re-introduced into a cassette. This system allows for compact and clean storage of the processed element until such time when it may be removed for additional prints or to interface with display equipment. Storage in the cassette is preferred to facilitate location of the desired exposed frame and to minimize contact with the negative during subsequent usage. U.S. Pat. No. 5,173,739 discloses a cassette designed to thrust the photographic element from the cassette, eliminating the need to contact the film with mechanical or manual means. Published European Patent Application 0 476 535 A1 describes how the developed film may be stored in such a cassette. The dimensions of such a so-called thrust cassette requires that the processed photographic element is wound tightly and under pressure, causing direct close contact between the front and back sides which results in ferrotyping, especially at high temperature and high relative humidity. Processing removable matte does not prevent this problem.
In recent years, rapid processing and high temperature drying after processing have become common practice for photographic materials. Films dried at high temperatures, for example 60.degree. C. (harsh drying), tend to be more prone to ferrotyping which results from close contact, especially under elevated humidity and temperature. When ferrotyping is sufficiently severe, the resulting prints are unacceptable. Films dried at lower temperatures, for example 40.degree. C. (mild drying), tend to show much less ferrotyping. The reason for this difference is not understood.
The reintroduction of processed photographic elements into thrust cassettes also causes scratches and abrasion marks on the side opposite to that containing matte particles. Such scratches and abrasion marks deface the photographic image quality and therefore very expensive retouching is often required.
Recently, significant advancements have been made with regard to the methods of preparing photographic material. For example, the speed of coating, finishing, and cutting has been increased. These improvements have also resulted in a significant increase in the amount of scratches and abrasion marks on the side opposite to that containing matte particles.
Moreover, recent improvements have also been made to the image quality of the photographic materials in regard to the nonuniformity, or graininess, of the resulting prints by improving the imaging layer structures (e.g., developed grains, dispersions, etc.). The graininess is generally measured by RMS granularity, wherein the variability of the density in a specific region of uniform exposure is measured. The definition of statistical variance in density can be found, for example, in "Introduction to Photographic Theory--The Silver Halide Process", Carroll, B. H., Higgins, G. C., James, T. H., published by John Wiley & Sons, 1980. The overall variance in density .sigma.(d) is given by EQU .sigma..sup.2 (d)=.sigma..sup.2 (image)+.sigma..sup.2 (matte)+.sigma..sup.2 (test)+error
where .sigma..sup.2 (image) accounts for the density variation due to image structures and .sigma..sup.2 (matte) accounts for the density variation due to the presence of matte particles. As reductions in the .sigma..sup.2 (image) have been made in recent years, the impact of the .sigma..sup.2 (matte) has become even more critical. It has been common to reduce the impact of the .sigma..sup.2 (matte) by reducing the specularity of the printing method, but this technique can limit the productivity of photographic printers. In addition, recent storage and display devices, such as PhotoCD and other means of electronic display all make use of specular transmission of the photographic element. Therefore, there is clearly a need to reduce the magnitude and impact of .sigma..sup.2 (matte) on image quality without sacrificing the ferrotyping protection offered by matting agents on the post process photographic element.